Recently, zirconium phosphate based inorganic ion exchangers have been utilized in various applications by virtue of their features. Zirconium phosphate based inorganic ion exchangers include amorphous ones, crystalline ones having a two-dimensional layer structure and crystalline ones having a three-dimensional network structure. Above all, hexagonal zirconium phosphates which have a three-dimensional network structure are excellent in heat resistance, chemical resistance and radiation resistance and low in thermal expansion, and are applied to immobilization of radioactive waste, solid electrolytes, gas adsorption/separation agents, catalysts, a raw material for antibacterial agents, and so on.
Hitherto, various hexagonal zirconium phosphates have been known. For example, there are AxNH4(1-x)Zr2(PO4)3.nH2O (for example, refer to Patent Document 1), AZr2(PO4)3.nH2O (for example, refer to Patent Document 2) and HnR1-nZr2(PO4)3.mH2O (for example, refer to Patent Document 3).
Also, zirconium phosphates which differ in a ratio of Zr to P have been known. For example, there are Na1+4xZr2−x(PO4)3 (for example, refer to Non-Patent Document 1), Na1+2xMgxZr2−x(PO4)3 (for example, refer to Non-Patent Documents 1 and 2) and Na1+xZr2SixP3−xO12 (for example, refer to Non-Patent Documents 2 and 3).
As methods for synthesizing these hexagonal zirconium phosphates, have been known a calcining method in which raw materials are mixed, and thereafter calcined at not less than 1000° C. using a calcining furnace to effect the synthesis, a hydrothermal method in which raw materials are mixed in water or in a state of containing water, and thereafter pressurized and heated to effect the synthesis, and a wet method in which raw materials are mixed in water, and thereafter heated at atmospheric pressure to effect the synthesis.
Above all, the calcining method makes it possible to synthesize zirconium phosphates with an appropriately controlled P/Zr ratio just by mixing raw materials and heating them at a high temperature. However, in the calcining method, uniform mixing of raw materials is not easy, and zirconium phosphate with a homogeneous composition is hardly made. Further, the calcining method requires pulverization and classification in order to obtain products in grain form after calcining, and thus it had problems in quality and productivity. Also, as a matter of course, crystalline zirconium phosphates containing ammonia cannot be synthesized in the calcining method. On the other hand, in the wet or hydrothermal method, a homogeneous microparticulate zirconium phosphate can be obtained, but no crystalline zirconium phosphates have been obtained except those having a P/Zr ratio of 1.5 and those indicated by the following formula (3) with a P/Zr ratio of 2.NH4ZrH(PO4)2  (3)
Ions such as of silver, copper, zinc, tin, mercury, lead, iron, cobalt, nickel, manganese, arsenic, antimony, bismuth, barium, cadmium and chromium have been known for a long time as metal ions that indicate antifungal, antibacterial and anti-algae properties (hereinafter, abbreviated to antibacterial metal ions). Especially, silver ion has been widely utilized as an aqueous silver nitrate solution which has effects of disinfection and sterilization. However, metal ions that show the above antifungal, antibacterial or anti-algae property are mostly toxic to human body, and thus there have been various limitations on methods of use, methods of storage, methods of disposing and the like, and applications also have been limited.
In order to exhibit the antifungal, antibacterial or anti-algae property, only a very small amount of antibacterial metal has to be allowed to act on an object of interest. Because of this, as antibacterial agents having the antifungal, antibacterial or anti-algae property, there have been proposed organic carrier based antibacterial agents in which an antibacterial metal ion is carried on an ion exchange resin, a chelate resin or the like, as well as inorganic antibacterial agents in which an antibacterial metal ion is carried on a clay mineral, an inorganic ion exchanger or a porous body.
Of the above various antibacterial agents, inorganic antibacterial agents are characteristic in that they are high in safety, long in durability of antibacterial effect, and also excellent in heat resistance, compared to organic carrier based antibacterial agents.
As one of the inorganic antibacterial agents, has been known an antibacterial agent comprising a clay mineral such as montmorillonite and zeolite in which alkali metal ions such as sodium ion have been ion-exchanged with silver ion. Since it has a skeleton structure based on the clay mineral itself which is inferior in acid resistance, it easily elutes silver ion and thus lacks durability of antibacterial effect, for example, in an acidic solution.
In addition, since the silver ion is unstable upon exposure to heat and light and immediately reduced to a metal silver, thereby causing coloring or the like, it had a problem in long term stability.
There has been one in which silver ion and ammonium ion are co-existent and carried on zeolite by ion exchange in order to enhance the stability of the silver ion. However, even in this case, prevention of coloring does not come to a practical level, and thus no solution has been given fundamentally.
Further, there have been other antibacterial agents in which an antibacterial metal is carried on an adsorptive charcoal. However, since these agents carry soluble antibacterial metal salts which physically adsorb or stick thereto, they rapidly elute antibacterial metal ions and thus lack durability of antibacterial effect when they are brought into contact with moisture.
Recently, an antibacterial agent in which an antibacterial metal ion is carried on a special zirconium phosphate salt has been proposed. For example, one represented by the following formula (4) has been known (for example, refer to Patent Document 4):M1M2xHyAz(PO4)2.nH2O  (4)wherein, in the formula (4), M1 is one selected from tetra-valent metals, M2 is one selected from a silver, copper, zinc, tin, mercury, lead, iron, cobalt, nickel, manganese, arsenic, antimony, bismuth, barium, cadmium or chromium, A is one selected from alkali metal ions or alkaline earth metal ions, n is a number satisfying 0≦n≦6, and x, y and z are numbers satisfying 0<(1)X(x)<2, 0<y<2, 0<z<0.5 and (1)X(x)+y+z=2, provided that 1 is the valence number of M2.
This antibacterial agent is known as a material which is chemically and physically stable, and shows antifungal and antibacterial properties for a long time. However, when this antibacterial agent is kneaded into a synthetic resin such as nylon, the resin is often colored as a whole so that it cannot be used as a product.    Patent Document 1: JP-A-H06-48713    Patent document 2: JP-A-H05-17112    Patent Document 3: JP-A-S60-239313    Patent Document 4: JP-A-H03-83906    Non-Patent Document 1: C. JAGER, and three others, “31P and 29Si NMR Investigations of the Structure of NASICON-Strukturtyps”, Expermentelle Technik der Physik, 1988, Vol. 36, 4/5, p 339-348    Non-Patent Document 2: C. JAGER, and two others, “31P MAS NMR STUDY OF THE NASICON SYSTEM Na1+4yZr2-y(PO4)3”, Chemical Physics Letters, 1988, Vol. 150, 6, p 503-505    Non-Patent Document 3: H. Y-P. HONG, “CRYSTAL STRUCTURE AND CRYSTAL CHEMISTRY IN THE SISTEM Na1+xZr2SixP3-xO12”, Mat. Res. Bull, Vol. 11, p-173-182